Process for preparing hydroxylamine from NO.sub.x -containing fl

Details Process for preparing hydroxylamine from NO.sub.x -containing fl Process for preparing hydroxylamine from NO.sub.x -containing fl

1994-04-21

1996-02-06

Langel, Wayne

Chemistry of inorganic compounds

Nitrogen or compound thereof

Oxygen containing

423235, G01B 2120

Patent

active

054894212

DESCRIPTION:

BRIEF SUMMARY
A process and device are disclosed for preparing hydroxylamine from NO.sub.x - and, possibly, O.sub.2 -containing flue gases. Nitrogen removal from the flue gases is combined with hydroxylamine synthesis by catalytic reduction of NO with hydrogen.
This invention makes it possible to combine nitrogen removal from flue gases, which is laid down by law in many countries for environmental reasons, with the commercial production of hydroxylamine, which represents a valuable intermediate product for the production of nylon-6.
Nitrogen removal from flue gases, especially from those found in industrial combustion installations, coal and crude petroleum power stations as well as in the preparation of azotic acids, is very important these days for environmental reasons and is in many countries subjected to strict statutory regulations. The EC guidelines, for instance, lay down that the nitrogen oxides content in the flue gases of industrial power stations and in industrial flue gases are not to exceed 200 to 400 mg/m.sup.3. These low limits cannot be observed by proper measures during the combustion process, the so-called primary measures, alone. It is therefore necessary to use a special process for the removal of undesirable nitrogen in so-called nitrogen removal processes in order to fulfil these high demands. The nitrogen removal process that is used the most at present is the nitrogen removal by selective catalytic reduction (SCR), in which the NO.sub.x (i.e. different nitrogen oxides, especially NO, possibly mixed with NO.sub.2) nitrogen oxides in the flue gases are catalytically reduced to N.sub.2 and H.sub.2 O in reaction with ammonia (NH.sub.3). This reaction usually happens at a temperature of 300.degree. to 400.degree. C. There are several other alternative industrial processes for nitrogen removal, but none of these processes transforms the undesirable nitrogen oxides in a technically acceptable product.
DE-PS 3 406 085 describes an attempt to produce an acceptable product, NO rich gas, during the purification of exhaust gases. It explains a process for nitrogen removal from NO.sub.x -containing flue gases by absorption of NO.sub.x nitrogen oxide in aqueous solutions of iron (II) salt with pH values of 0 to 1. However, since the solubility of NO.sub.x in such a solution is known to be extremely low, this process is not workable enough for industrial nitrogen removal.
Other processes have also been suggested in which SO.sub.x and NO.sub.x are removed from flue gases or other absorbent, like Mg(OH).sub.2, Na.sub.2 SO.sub.3, citrates and suchlike, are used as absorbing agents (cf. H. Hasui and H. Omichi, "The Mitsui Wet Process for SO.sub.2 and NO.sub.x Removal," Nenryo Kyokai-Shi 55 (1979) 4, 264 to 269; E. Sada, H. Kumazawa, I. Kudo and T. Kondo, "Ind. Eng. Process Des. Dev.," 20 (1981) 3, 46-49; E. Sada, H. Kumazawa, Y. Sawada and T. Kondo, Ind. Eng. Process Des. Dev., 21 (1982) 4, 771-774, and W. Weisweiler, B. Retzlaff and L. Raible, Chem. Eng. Process, 18 (1984) 85-92).
When using absorbents like those the chemical equilibrium is moved to the desired side. At the same time, however, an undesirable oxidation of iron (II) to iron (III) occurs on the basis of the oxygen contents found in all flue gases, which strongly reduces the absorbing power of the absorbent. In addition sulphates form, and their removal is problematic. Normally unhydrated lime is added and potassium sulphate is obtained by precipitation. The Fe(EDTA) complex is lost, however.
On the other hand hydroxylamine (NH.sub.2 OH) is generally recognized to be a valuable intermediate product for nylon-6 synthesis.
Hydroxylamine is used to prepare cyclohexanonoxim out of cyclohexanone, in which the resulting cyclohexanonoxim is transferred to caprolactam through the Beckmann rearrangement. This caprolactam can be polymerized into a polyamide, namely nylon-6, an extraordinarily valuable synthetic substance.
Therefore it has been a long-lasting endeavor to prepare the hydroxylamine necessary as intermediate material for the preparation of nylon-

REFERENCES:
patent: 4013430 (1977-03-01), Adachi et al.
patent: 4091074 (1978-05-01), Gorai et al.
patent: 4126529 (1978-11-01), DeBerry
patent: 4879102 (1989-11-01), Hoppe et al.
patent: 5320816 (1994-06-01), Tsai et al.

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